Diffusion

• What is the primary method of exchange across cell membranes?

  • Diffusion
• Does diffusion require energy?

  No, diffusion is a passive movement of particles and does not require energy.
• In which direction do particles move during diffusion?

  Particles move from an area of high concentration to an area of low concentration.
• When does net movement stop in diffusion?

  Net movement stops when the particles are evenly distributed.
• Which gases diffuse easily through cell membranes?


  Oxygen and carbon dioxide diffuse easily.
• What non-polar molecules soluble

  • Lipid soluble
  • Very small in size
• Are polar molecules larger or smaller than non-polar molecules?

  Polar molecules are larger than non-polar molecules.
• How do molecules move during simple diffusion?

  Molecules diffuse directly through the cell membrane.
• What is facilitated diffusion?

  • Requires carrier proteins
  • Uses protein channels
• What type of molecules diffuse slowly through the bilayer?

  Ions and polar molecules, such as amino acids and glucose, diffuse slowly.
• How do charged particles cross the cell membrane in facilitated diffusion?

  They diffuse through carrier or channel proteins.
• What two kinda of particles require facilitated diffusion?

  They are charged particles and water soluble.
• What are the three steps of facilitated diffusion using carrier proteins?

  1. Large molecule attaches to a carrier protein.
  2. Protein changes shape.
  3. This releases the molecule on the other side of the membrane.
• What is the function of channel proteins?

  • Form pores in the membrane
  • Allow charged particles to diffuse through
• On what factors does facilitated diffusion depend?

  • Concentration gradient
  • Number of channel/carrier proteins
• What factors increase the rate of simple diffusion

  A higher concentration gradient

  Decrease in thickness of exchange surface

  Increased surface